Inefficient buildings are a major cause of wasted energy, a problem that is being addressed by better materials and better ways of managing heating, cooling, and lighting. For example, some window materials can allow outside light in (cutting the need for lighting) while blocking infrared light (in turn cutting the need for air conditioning). But those are fixed solutions. If you want to let more warmth in on a cold day, they're not going to help.

The solution is a smart material, one that can adjust according to the building's needs. In the most recent issue of Nature, some researchers at Lawrence Berkeley National Laboratory (joined by a colleague in Spain) report on just such a material. By passing a voltage through a specially designed glass, the researchers can switch it among three states: completely transparent, blocking infrared light, or blocking both infrared and visible wavelengths.

The new glass was based on the team's earlier work on indium-tin-oxide (ITO) nanocrystals. This material is able to absorb near-infrared light, but only if it's in the right electronic state (the ability depends on having enough free electrons around). Since glasses aren't crystalline materials, ITO crystals are inappropriate for use in this application, at least in bulk.

For the new material, the authors figured out a way to embed the nanocrystals in an amorphous material, making a hybrid that has the properties of a glass in terms of transparency to a wide range of wavelengths. They first chemically linked the nanocrystals to a coating that contained niobium and then packed them at a high density. At that point, they chemically converted the niobium compound to a niobium oxide, which formed an amorphous glass. This process gave them control over factors like the density of the nanocrystals within the glass, allowing them to try a number of combinations of the material.

Just like the nanocrystals themselves, the resulting material showed an ability to block near-infrared light that depended on their electronic state. By switching the voltage across the glass from 4V to 2.3V, they could switch it from being transparent to infrared to blocking these wavelengths.

As they dropped the voltage further, an additional change took place, one that altered the oxidation state of the niobium. When the voltage difference reached 1.5V, the changes in the material's structure that resulted from the alterations in oxidation state blocked visible light as well.

That's the good news; the bad news is that there are still a few things that need to be worked out before this gets put into production. For example, the window acts like a battery in many ways, as it needs a lithium electrode, and lithium ions diffuse into the material when the voltage changes. It has better durability than many batteries—keeping 96 percent of its performance even after 2,000 cycles—but we certainly don't want a battery with reactive materials like lithium and an electrolyte coating a large office tower.

The authors also don't say how long the material holds its voltage on its own. Depending on how often you have to recharge the material in order to keep it in the state you want, it might not actually save energy in the end.

The final issue is the raw materials. Niobium is relatively inexpensive, but indium has found use in a lot of electronics applications, and its price has spiked to over $1,000 a kilogram in recent years (niobium has been quite a bit cheaper). Unless very, very little of the glass' weight comes from indium, we're probably not going to want to coat an office tower with it.

Still, the nice thing about this new glass is that the authors understand some of the electronic properties that make it work, as well as the production techniques that make it into a functional glass. Hopefully, someone can figure out a more abundant and cheap material that can act similarly.

55 Reader Comments

Pretty cool. If it's fast, it may also be the foundation for a new e-ink technology. On the down side, it seems to work by switching between absorbing the light energy and transmitting it. For building applications, switchable reflection might be more useful.

in principle (oversimplification) it seems like the parallax barrier that 3DS use. When electricity runs thru, it blocks.

but those glass, seems wont be practical for developing countries. Electricity are a main comodity that often goes out in random times. It will be super annoying when you need to make the glass block light in noon but the theres electricity blackout.

Pretty cool. If it's fast, it may also be the foundation for a new e-ink technology. On the down side, it seems to work by switching between absorbing the light energy and transmitting it. For building applications, switchable reflection might be more useful.

Wouldn't it be simpler to just apply a coating like photochromic eyeglass lenses (aka Transitions) use? No power needed. Some types offer polarizing effects. You can't block all light with Transitions, obviously, but it could be a good alternative for many applications. Is this tech too expensive or non-scalable for window-sized applications maybe?

They talk about "blocking" IR, which implies absorption. This is better than the light penetrating into the room, but you still have an energy transfer onto the surface of the building. For cooling purposes, reflectivity is what you want.

I've been waiting so long for this kind of technology. My appartment is either almost always too hot or too cold. My wife doesn't like keeping windows open and I don't like having the AC on all the time. This seems like it could solve both our problem. Man I love living in the future.

Wouldn't it be simpler to just apply a coating like photochromic eyeglass lenses (aka Transitions) use? No power needed. Some types offer polarizing effects. You can't block all light with Transitions, obviously, but it could be a good alternative for many applications. Is this tech too expensive or non-scalable for window-sized applications maybe?

Probably useful in really warm climates, but in many places you would want the exact opposite effect during the winter to maximize warming from the sun. The ability to control these phases to optimize what you need during that season is what makes this compelling.

Wouldn't it be simpler to just apply a coating like photochromic eyeglass lenses (aka Transitions) use? No power needed. Some types offer polarizing effects. You can't block all light with Transitions, obviously, but it could be a good alternative for many applications. Is this tech too expensive or non-scalable for window-sized applications maybe?

I think the main advantage of this new tech is to have adjustable IR transparency, blocking IR transmission when it's hot (reducing the load on the air conditioning), but allowing more IR when it's cool (reducing the load on the heating system).

I imagine it would be possible to make a photochromic / "Transitions"-type material tuned to IR wavelengths vs. visible light. if there was a way to make such a material react differently based on temperature - becoming more transparent to IR at lower temperatures, and less transparent at higher ones, without electricity - that would be awesome.

I wish it weren't the case that getting published in Nature = Very cool stuff that you can forget about going down to buy at Home Depot anytime soon.

I guess if basic research generated products quickly we wouldn't have to constantly justify the budget for it with the bean counters.

It's fantastically neat, and wonderful foundational research that's gone quite far in a great direction... but the article outlines the pitfalls (and remaining questions) pretty clearly. As impressive as what they've achieved is, it's quite clearly not anything ready for commercial production and use: at least, not in the envisioned scenario of use in buildings. This is why science simply can't be budgeted only on end results. These ultimately impractical yet essentially functional (or even merely theoretical) middle stepping grounds are exceptionally significant to ever achieving end goals.

Wouldn't it be simpler to just apply a coating like photochromic eyeglass lenses (aka Transitions) use? No power needed. Some types offer polarizing effects. You can't block all light with Transitions, obviously, but it could be a good alternative for many applications. Is this tech too expensive or non-scalable for window-sized applications maybe?

I believe the eyeglass coating that reacts to sunlight has longevity problems. It yellows the glass after multiple years and the transition effect lessens over time as well. This is suitable for eyeglasses that generally get replaced every few years, but not for buildings where the glass panes might not be replaced for more than 50 years.

Why is required energy a concern?If energy is required by these guys to block sunlight/IR on a sunny day, guess what: It's a sunny day. Just add photovoltaic cells. Voltage seems low enough, and hopefully amperage is a non issue.

Automobile windows! Tinted windshield on-demand when driving into the sunset!

I think I'm actually salivating...

Would be a potential regulatory pain since maximum allowed tint levels are set at the state level and not all are equal.

couldnt the max just be set when the glass is installed at the dealer? I mean this would probably be an expensive add on.

... and if you move out of state, buy a used car originally sold out of state....

NTM if it's software configurable some idiots will rig a way to do so beyond what's locally allowed. Yeah they can do it now if they really try; but current tinting options aren't easy to apply well so it'd be a much more pervasive problem.

They talk about "blocking" IR, which implies absorption. This is better than the light penetrating into the room, but you still have an energy transfer onto the surface of the building. For cooling purposes, reflectivity is what you want.

If it were used on the outside pane of a multipane window, then the heat would still be stopped before it reached the inside (or at least slowed down more that it would otherwise).

A designer can actually design the system so that it allows sunlight to hit the glass and heat the building in winter (heat it) and block sunlight from reaching the glass in summer - especially with building modeling which tracks sun angles based on GPS coordinates.

The only place I'm guessing this glass would be remotely affordable is in a commercial building... Dont forget, the glazing contractor installs the glass, then an electrician has to come wire the glass up to the main electrical panel. Those buildings already uses double/triple glazed low-e coated, tinted, argon filled glazing. I cannot really see how this would be cost effective vs good design and what's already available for cheap. Most construction costs are paying for labor, and paying an electrician to wire up your glass seems expensive.

And for the guy asking to tint his windshield - 3M Crystalline tint is 99.5% transparent and has excellent heat rejection. You can tint your windshield with it and no one will know its there unless it delaminates. It skirts state laws because of how transparent it is.

Wouldn't it be simpler to just apply a coating like photochromic eyeglass lenses (aka Transitions) use? No power needed. Some types offer polarizing effects. You can't block all light with Transitions, obviously, but it could be a good alternative for many applications. Is this tech too expensive or non-scalable for window-sized applications maybe?

You are missing the point. The goal is not to block light, the goal is - to block (or not block) infra-red- under my control.Photochromic devices don't offer control --- they block in the presence of lots of light regardless.

The point is:SUMMER: light comes in the house/car, bounces around inside, gets converted to IR. Glass is not transparent to IR, so the heat builds up until other mechanisms allow heat transfer. This is because normal glass is opaque to IR. SO why not invent glass that is transparent to IR? BecauseWINTER: light comes into the house/car, bounces around, gets converted to IR, helps warm things up some. Now it is a feature, not a bug, that the glass is opaque to IR.

A designer can actually design the system so that it allows sunlight to hit the glass and heat the building in winter (heat it) and block sunlight from reaching the glass in summer - especially with building modeling which tracks sun angles based on GPS coordinates.

The only place I'm guessing this glass would be remotely affordable is in a commercial building... Dont forget, the glazing contractor installs the glass, then an electrician has to come wire the glass up to the main electrical panel. Those buildings already uses double/triple glazed low-e coated, tinted, argon filled glazing. I cannot really see how this would be cost effective vs good design and what's already available for cheap. Most construction costs are paying for labor, and paying an electrician to wire up your glass seems expensive.

And for the guy asking to tint his windshield - 3M Crystalline tint is 99.5% transparent and has excellent heat rejection. You can tint your windshield with it and no one will know its there unless it delaminates. It skirts state laws because of how transparent it is.

You have some good points in there, but this or similar technology still adds value. This may not be the tech that makes it into average homes, but any interest it provokes will fuel investment into other solutions.Some of the ways this tech adds value over overhangs:It is a lot easier to automate vs shutters or curtains.Provides radiant barrier insulation for unseasonably warm fall/spring days while retaining visibility.Provides automatic privacy when it is dark outside, also theoretically allowing less light loss as well.Provides radiant barrier insulation at night in cool/cold days and dark days (no solar gain)..

They talk about "blocking" IR, which implies absorption. This is better than the light penetrating into the room, but you still have an energy transfer onto the surface of the building. For cooling purposes, reflectivity is what you want.

You people are all missing the point. IR INTO a building is not the primary heating mechanism. Look at the spectral power density curve for the sun. The energy is all in the visible range.

The issue is not blocking IR coming INTO the building (glass already does that), it is ALLOWING IR OUT of the building (in summer) and then preventing it from leaving in winter.

You COULD make your building cooler in summer by letting less light in (and of course that's what things like blinds are for) but you often want the light in the building (or car), you just don't want the heating that goes with it (because once the light is in the building, it bounces around, gets absorbed, and thermalizes).

A designer can actually design the system so that it allows sunlight to hit the glass and heat the building in winter (heat it) and block sunlight from reaching the glass in summer - especially with building modeling which tracks sun angles based on GPS coordinates.

The only place I'm guessing this glass would be remotely affordable is in a commercial building... Dont forget, the glazing contractor installs the glass, then an electrician has to come wire the glass up to the main electrical panel. Those buildings already uses double/triple glazed low-e coated, tinted, argon filled glazing. I cannot really see how this would be cost effective vs good design and what's already available for cheap. Most construction costs are paying for labor, and paying an electrician to wire up your glass seems expensive.

And for the guy asking to tint his windshield - 3M Crystalline tint is 99.5% transparent and has excellent heat rejection. You can tint your windshield with it and no one will know its there unless it delaminates. It skirts state laws because of how transparent it is.

Cars strike me as a more useful immediate commercial target than buildings. There are generally better solutions for buildings (though, of course, many of those require the building to have been designed by someone who was not a moron, so retrofitting moron designed buildings may be better than the alternative options).

Think about the failure mode... It requires voltage to maintain transparency.This is something that should _not_ be in a car windshield as-is.

I am not sure it needs a continuous voltage. The story says that "96 per cent of charge capacity retained after 2,000 cycles", which wouldn't make sense if it needed a continuous charge. Though as the Ars summary says, we don't know "how long the material holds its voltage on its own".

Edit: also, the picture provided shows it working without any obvious wires

I thought of this concept in the 70s, of course not realizing that you just patent concepts (which seems stupid to me)seehttp://arstechnica.com/tech-policy/2013 ... e-patents/I also went one step further, when you dial up the dark you convert the sunlight via PV. I did nothing.I could have been rich, dammit!

Just like the nanocrystals themselves, the resulting material showed an ability to block near-infrared light that depended on their electronic state. By switching the voltage across the glass from 4V to 2.3V, they could switch it from being transparent to infrared to blocking these wavelengths.

There is no information about the operating temperature range or durability, or cost, but I would think that this would be great for car windows, ideally powered by solar cells. It would keep the car much cooler and save gas as the A/C would not be needed as much.

But I imagine that this is one of those expect production in 10 years or so kind of things at this point.

How is a material that "can allow outside light in, while blocking infrared light" supposed to reduce my air conditioning needs when that's the exact reason my car is so hot on sunny days? (It's also called "the greenhouse effect" when atmospheric gases do exactly the same thing.)

I'm pretty sure you want it to block the visible light coming in (so it's not absorbed and converted to heat there), or be transparent to the infrared going out.

Wouldn't it be simpler to just apply a coating like photochromic eyeglass lenses (aka Transitions) use? No power needed. Some types offer polarizing effects. You can't block all light with Transitions, obviously, but it could be a good alternative for many applications. Is this tech too expensive or non-scalable for window-sized applications maybe?

Probably useful in really warm climates, but in many places you would want the exact opposite effect during the winter to maximize warming from the sun. The ability to control these phases to optimize what you need during that season is what makes this compelling.

Yup. My house is decently sited with a modest overhang. It faces south south east for the rear of the house. So in the summer time I really only get direct sun from sun up until about 10am and the front of the house is well shaded, so sun exposure is limited to only about 90 minutes to 30 minutes before sunset. During the hotest part of the day, the roof overhang shades the windows from about 10-3 and then in the afternoon the trees shade the side/front of the house. In the winter time I have sun in the rear windows/side windows from sun up pretty much till sun down with some being a bit blocked by a tree in the side yard for part of the day (but the leaves are off it, so it is only partial shade) and around high noon there isn't too much that gets in (but some limited direct sun).

It probably wouldn't be much gain for me, but I'd still probably jump on windows like this. Especially if you could make an infrared photoreflective layer that can be switched on and off, that would be of a huge benefit for both reflecting infrared light trying to come in in the summer, but also at night time or the indirect light windows, reflect infrared light from the house back IN (well, low e windows kind of do this already, but this might enhance the effect).

It would also be cool to simply black out your windows. Easier than curtains. If this is all cheap and low power (IE you could battery power it, or heck, have a battery and a very small solar cell on the outside window frame to power it), you could have lots of other uses. Shower doors/glass that you can black out for privacy. Vehicle glass you could (at least when not driving) double as privacy glass or reduce solar heating in the summer when parked.

How is a material that "can allow outside light in, while blocking infrared light" supposed to reduce my air conditioning needs when that's the exact reason my car is so hot on sunny days? (It's also called "the greenhouse effect" when atmospheric gases do exactly the same thing.)

I'm pretty sure you want it to block the visible light coming in (so it's not absorbed and converted to heat there), or be transparent to the infrared going out.

Because roughly 50% of the sunlight is emmitted in the infrared spectrum and most of it is in the short infrared wave lengths. Glass blocks the long infrared wave lengths pretty well...which is what warm things give off. That is how it acts like a greenhouse.

Glass lets the visibile and short infrared in, which heats things up, which emmitt long infrared, which is then blocked by the glass, heating the thing up. If you block just the short infrared, you effectively reduce the heating of the car by 50% (or house). I can see how it would be worth while to cut how much energy is coming in through the glass of my car or house by 50%.

Of course if you are parking your car, reducing it by 100% would be even better, so black it out in visible AND infrared (but only when parked).

I know right? A graphic credited to the Lawrence Berkeley National Laboratory showing an actual piece of material that is being described, indeed in two of it's three possible states, conveys absolutely no meaningful scientific context to this article. /s

How is a material that "can allow outside light in, while blocking infrared light" supposed to reduce my air conditioning needs when that's the exact reason my car is so hot on sunny days? (It's also called "the greenhouse effect" when atmospheric gases do exactly the same thing.)

I'm pretty sure you want it to block the visible light coming in (so it's not absorbed and converted to heat there), or be transparent to the infrared going out.

I'm pretty sure you're just not fully thinking it through.

Equivalent amounts of visible spectrum daylight and visible spectrum artificial light will heat equally; so sunlight vs your lamps are equal. But sunlight on the surface is 45% visible light and 55% IR which is significantly better than your LED or CFL bulbs which are only 20-25% efficient; or to put it another way your lamps put out about 3x as much IR as the sun does for an equivalent amount of light. This means sunlight heats your house a lot less than your lamps do so you want to let enough sunlight in to light your rooms.

As for keeping or releasing IR, if it's hotter outside than inside more black body IR will be trying to enter than leave; and an IR opaque window will keep out most of the direct IR from the sun itself so you want IR blocking.

I depends on the building. I priced a retractable shady canopy for my back desk -- ack! New windows were cheaper (although not a related project). And for commercial buildings, canopies on every window would be a maintenance nightmare.

I know right? A graphic credited to the Lawrence Berkeley National Laboratory showing an actual piece of material that is being described, indeed in two of it's three possible states, conveys absolutely no meaningful scientific context to this article. /s

Oh, they must be your hands in those gloves. Such lovely hands. Did I offend? /sIf you want to convey science, wear latex gloves. If you want to convey medical, get some 40-ish slightly greying guy in a white lab cost with a stethascope around his neck. If you want to convery good times and sports, get a bunch of mixed culture, shapely young folks standing around a grill. See my point? You were looking at the material. I was looking at the blocking, layout, and presentation of the photo, which believe it or not I find more interesting. But that's just me. As I said above ......"just sayin".

I would think that glass that just absorbs IR would be of great interest to car manufacturers. Reflecting it would be better, of course, but if the windows absorb the heat that's that much less that penetrates to the seats, dash, and steering wheel when parked. At least on the windows natural convection and wind can work to cool the surface.

The windows as presented may also be of interest in cars. Lots of people commute North/South in the mornings and afternoon. It's not always possible to position the shade to safely block the sun. Imagine if your window was broken into addressable sections and could darken only the parts necessary to shade the driver's eyes without reducing visibility of the rest of the road.